José Guízar is fixated on a window into New York life that other people might look right past — actual city windows.

Ramsay de Give for The Wall Street Journal

José Guízar is pictured in SoHo. The 26-year-old graphic designer has created the website Windows of New York. See more photos.

Mr. Guízar, a 26-year-old graphic designer, has created a website featuring nothing but his colorful illustrations of the shuttered, barred and even air-conditioner-covered windows that have caught his eye around the city.

A New Yorker for only a year, Mr. Guízar said he started drawing the largely unnoticed building feature because he never wants to overlook the city’s architectural quirks. “We get so used to our routine that we walk the same street every day and take the same train and we forget what’s around us,” he said.

The images on his oddly soothing website, Windows of New York, begin as photographs of windows that he finds striking, like a green trimmed one on Christopher Street with a small flower box. Mr. Guízar then creates a version of each window using Adobe Illustrator, drawing on his design skills in his day job at a mobile-app company.

“I’m not looking for the most iconic windows or even the most beautiful,” he said. “Just interesting windows.”

Walking around the streets of SoHo on a recent morning, Mr. Guízar pointed to a window that piqued his interest on the fourth-floor of an inconspicuous brick building, a fire escape zigzagging across its pale pink facade. The window had blinds drawn and a grubby air conditioner, with what looked like a yellow metal bar resting diagonally against the window pane.

He refrains from looking inside the windows he photographs—“I’m not a creeper,” he said—but often wonder if the unknown stories on the other side of the glass is what makes the project resonate with people.

To compose illustrations for his website, Mr. Guízar sets the windows against a monochromatic background and uses only a few colors. The bright backgrounds, he says, are a nod to the architecture in his native Mexico, where he saw old houses in shades of “neon green, pink and blue.”

Mr. Guízar said he is drawn to this style because he prefers minimalism and simplicity in his work, calling those qualities “the very basics of graphic design.”

“The hardest part is to get something so static and make it look alive,” said Mr. Guízar, whose project has been picked up by several blogs.

The illustrations are accompanied by the address of the building. “It makes the windows real, people can relate to them,” he said.

It also means residents who look out from those panes can appreciate their windows in a new way.

Jacob Cass, 25 and also a graphic designer, was surprised when he stumbled upon a window from his Hell’s Kitchen apartment building — “minus the grime and dust” — while visiting Mr. Guízar’s website.

A New York transplant as well, he understands why the illustrator is drawn to a simple architectural feature. “In terms of windows and the styles of apartments, there’s something about the different types,” Mr. Cass said. New York windows “are a bit more memorable than in other places.”

Ideally, Mr. Guízar would love to see his window illustrations in print, displayed one page at a time. But for now he’s working on creating a collection of up to 100 illustrations for the website.